The present invention relates to a method for operating an internal combustion engine of a motor vehicle, for example, in which fuel is injected into a combustion chamber in a rich mode of operation and a lean mode of operation, switching between the rich and lean modes of operation, and nitrogen oxides are stored in a catalyst. The present invention also relates to a corresponding internal combustion engine and a control unit for an internal combustion engine.
An internal combustion engine and a control unit may be used to direct gasoline injection, for example, fuel may be injected into a combustion chamber of the internal combustion engine during the intake phase in a rich mode of operation, e.g., in homogeneous operation or during the compression phase in a lean mode, e.g., in stratified charge operation. Homogeneous operation may be provided for full-load operation of the internal combustion engine, while stratified charge operation may be suitable for idling and partial load operation. With an internal combustion engine having direct injection, the two modes of operation described above may be switched between, e.g., as a function of a desired setpoint mode of operation.
NOx components, i.e., nitrogen oxides, may be present in the exhaust gas in lean stratified charge operation, for example, and may not be aftertreated by a three-way catalyst. For this purpose, a storage catalyst may be provided that stores the nitrogen oxides, converts the oxides in a subsequent rich operating mode of the internal combustion engine, and then releases them again. Since the storage capacity of the storage catalyst is limited, it should be loaded and unloaded constantly. This may be controlled and/or regulated using a lambda sensor upstream from the catalyst, for example, by modeling the storage capacity of the storage catalyst.
Due to aging of the internal combustion engine, changes may occur in the modeling, and thus there may be errors. These errors may cause a permanently defective control and/or regulation of the loading and unloading of the storage catalyst.
An object of an exemplary embodiment and/or exemplary method according to the present invention is to provide a method for operating an internal combustion engine, with which the loading and unloading of the storage catalyst is controlled and/or regulated correctly, even over a long period of time.
An exemplary method according to the present invention may achieve this object by determining a quality function for the storage of nitrogen oxides in the catalyst, the switching between the operating modes being influenced as a function of the quality function. This object may be achieved using an internal combustion engine and a control unit.
The quality function may have a declining characteristic, due to aging or poisoning of the catalyst. If this declining characteristic changes, whether a change has occurred in the internal combustion engine may be deduced, e.g., due to aging. If this occurs, the model for switching between the operating modes of the internal combustion engine may be adapted, so that the quality function develops into a declining characteristic again.
Aging phenomena of an internal combustion engine may be detected on the basis of the quality function and may be considered by the control unit accordingly.
In an exemplary embodiment and/or exemplary method according to the present invention, the quality function is determined as a function of the period of time, after which a rich mode of operation breaks through the catalyst. Breakthrough of the rich mode of operation may be detected using a lambda sensor situated downstream from the catalyst, for example. The breakthrough indicates that the catalyst has released all the NOx stored components and that reducing agents, in the form of xe2x80x9crichxe2x80x9d exhaust gas, have reached the downstream lambda sensor. The period of time described above is a measure of the storage capacity of the catalyst. Over time, the duration of the period of time becomes progressively shorter, representing the aging and/or poisoning of the catalyst.
In another exemplary embodiment according to the present invention, the quality function is determined as a function of a plurality of successive periods of time. The change in the quality function over time is thus considered.
In another exemplary embodiment according to the present invention, a change in a slope of the quality function curve is determined. A change in the internal combustion engine, due to aging, may be deduced, for example, on the basis of the change in slope of the quality function curve.
It is believed to be advantageous if the-switching between modes of operation is adapted. The loading and/or unloading times for the storage of nitrogen oxides in the catalyst may be adapted.
In an exemplary method according to the present invention, which may be performed by a control element of a control unit of an internal combustion engine, for example, in a motor vehicle, and a program, which runs on a computer, for example, on a microprocessor, and which is suitable for executing an exemplary method according to the present invention, is stored on the control element. Thus, the exemplary method according to the present invention is implemented by a program stored on the control element, so that the control element, provided with the program, performs, in the same way, as an exemplary method according to the present invention. An electric storage medium, such as, for example, a read-only memory or a flash memory, may be provided as the control element.